Abstract
Robust genetic progress and positive response to selection occurred in growth rate. The tangible increase in the genetic trends for early ADG and KR over the 40 years. Presence of additive genetic variation specifies selection that favors higher gain. KR has high genetic and phenotypic correlation with ADG for Avikalin sheep. KR as selection criterion will produce fast growing animals with limited resources. Avikalin sheep has been developed for higher growth rate and wool yield, however, wool has lost its market value over time. The aim of the study was to know the genetic potential of Avikalin for growth and also to suggest a selection criterion for higher growth with feed conversion efficiency. A total of 6296 animals descended from 2048 dams and 390 sires spread over a period of 41 years (1976–2016) at ICAR-Central Sheep and Wool Research Institute (CSWRI), Avikanagar were used for the analysis. Genetic trends were obtained for average daily gain (ADG) from birth to weaning (ADG1), weaning to 6-month (ADG2), 6-month to 12-month (ADG3) and Kleiber ratios of corresponding age (KR1, KR2 and KR3) in crossbred Avikalin sheep. Co(variance) components and genetic parameters were estimated by univariate and bivariate animal models using the average information restricted maximum likelihood (AIREML) by excluding or including maternal genetic or maternal permanent environmental effects. Significant and high additive genetic variances were observed for all the traits. Decreasing trends were observed for maternal effects as age advances. The genetic trends for ADG and KR up to 6 month age were positive and had substantial increment over the years indicating the impact of selection that favored higher gain in body weight at early ages. However positive and desired genetic trend at early ages (≤6 months), had an inverse relationship with genetic gain or trend at a later age (>6 month). Moderate estimates of the total heritability ( h T 2 ) 0.14, 0.18, 0.11, 0.19, 0.13 and 0.14 were obtained for ADG1, ADG2, ADG3, KR1, KR2 and KR3, respectively. This indicates the scope of direct selection for these traits for further improvement. The positive and desired genetic and phenotypic correlations between ADG and their corresponding KR suggested the scope of indirect selection for growth rate if lambs are selected for higher feed efficiency based on KR.
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